Niobium Doping Research Articles

Aliovalent Doping of Niobium and Tantalum Pentoxide as Potential Alternative Support Material for Fuel Cell Catalysts

AbstractAs the usually used Carbon Blacks (CB) as support materials in fuel cell catalysts are thermodynamically unstable, alternative supports with high chemical stability and electrical conductivity are to be found. After the investigation of Nb and Ta‐doped SnO2 in an earlier publication, which revealed interesting conductivity properties, we expanded our portfolio of mutual doping of elements of stable oxides into the oxides of the others by reporting here on the Sn, Hf and W‐doping as guests into the base oxides Nb2O5 and Ta2O5. The changes in unit cell parameters as indicators for the doping success were investigated in the doping range of x=0–10 mol % guest fraction. From a complete solubility of the guest ions in case of Hf and W‐doping in the base oxides to a limited solubility in case of Sn‐doping, a whole spectrum of different results was obtained. Additional insight came from UV/vis spectroscopic investigations in diffuse reflectance as well as electrical conductivity measurements.

Electronic Structure Modulating of W 18 O 49 Nanospheres by Niobium Doping for Efficient Hydrogen Evolution Reaction.

Developing efficient electrocatalysts to reduce HER overpotential is vital to enhance hydrogen production efficiency and minimize energy consumption. Adjusting the electronic structure of transition metal oxides via elemental doping is a potent strategy to improve the effectiveness of electrocatalysts for hydrogen evolution. In this work, we synthesized a set of niobium-doped tungsten oxides (Nbx-W18O49) under anoxic conditions using a straightforward "one-pot" solvothermal approach. After doping Nb, the oxygen vacancy content inside W18O49was increased, which induced a synergistic effect with the active sites of tungsten. In acidic environments, the hydrogen evolution activity of the Nb0.6-W18O49electrocatalyst is secondonly by 20 wt% Pt/C. It attains a current density of -10 mA cm-2at an overpotential of 102 mV. By comparison with W18O49, Nb0.4-W18O49and Nb0.5-W18O49, Nb0.6-W18O49demonstrates a reduced charge transfer resistance, which significantly enhances its conductivity and the speed of electron movement across interfaces. Coupled with this feature are notably faster HER kinetics. Additionally, it exhibits excellent stability, meaning it maintains its performance and structural integrity over prolonged periods and under various operational conditions. This article provides a new perspective for discovering inexpensive and efficient hydrogen evolution electrocatalyst materials.

Enhanced cyclability and energy density of mid-nickel layered oxide cathode material LiNi0.55Mn0.25Co0.20O2 by niobium doping via solvothermal method

Ni-based layered oxide materials are among the most promising cathode materials for the next generation of lithium-ion batteries due to their higher energy capacity. However, capacity decay occurs due to degradation mechanisms that reduce the electrochemical performance of this type of material. This work aims to synthesize Nb-doped LiNi0.55Mn0.25Co0.20O2 (Nb-NCM) materials via the solvothermal method to enhance the cyclability and energy density of the layered oxide cathode. The effects of Nb doping on the microstructure and the electrochemical performance of the cathodes are investigated. The introduction of the contents of Nb expands the structural lattice parameters and decreases the Li+/Ni2+ cation mixing degree of the NCM cathode. Furthermore, the Nb doping enhances the electrochemical activity of LiNi0.55Mn0.25Co0.20O2, increasing its initial discharge capacity to 169.61 mAhg−1 when 1% of Nb was used as a dopant (1%Nb-NCM) in contrast to the capacity of 149.45 mAhg−1 presented by the pristine material. The modified 1.0%Nb-NCM material also exhibits remarkable cycling performance with a capacity retention of 92.7% after 100 cycles at the rate of 1 C (2.8–4.3 V). This work suggests a rational strategy for high-performance cathode for lithium-ion batteries, proposing the extension of Nb doping to enhance Ni-mid material's cyclability.

Niobium doping as a pathway for tuning the optical properties of cobalt ferrites

In this work, the effect of niobium pentachloride concentration (NbCl5) and the influence of the pentavalent niobium ion on the structure and optical properties of cobalt ferrites was studied for the first time. The sol-gel method was applied to synthesize the xerogel with a subsequent heat treatment at 550 °C for 2.5h to obtain the nanoparticle. X-ray diffraction showed the expected spinel phase in all samples. Thus, it was possible to observe a shift in the main reflection (311) and a change in the lattice parameter as the niobium content increased. The crystallite size varied between approximately 18 and 34 nm. The Raman spectra showed typical vibrational modes of cobalt ferrite with no indication of secondary phase modes and variation in the A1g(2) and T2g(1) bands related to the octahedral and tetrahedral sites, respectively. Moreover, there is a correlation to an observed redshift, indicating an increase in the degree of inversion. Diffuse reflectance showed that the band gap of the samples varied from 1.99 eV for the pure sample (Co1.0Fe2.0O4) to 1.6 eV for the highest doping content (Co1.0Nb0.1Fe1.90O4). The coercivity was also affected, ranging from 1253 Oe in the pure sample (Co1.0Fe2.0O4) to 745 Oe in the doped sample (Co1.0Nb0.1Fe1.90O4). These results prove that the optimization of properties was successful since there was a marked decrease in the band gap and an increase in UV absorption. This result shows that it is possible to optimize the optical properties by introducing niobium, an effect that has not been possible in other studies with this type of dopant.

Ultrafast and Highly Efficient Sodium Ion Storage in Manganese‐Based Tunnel‐Structured Cathode

AbstractNa0.44MnO2 with tunnel structure is considered a promising low‐cost cathode material for sodium‐ion batteries. However, the sluggish Na+ transport kinetics and low initial Coulombic efficiency restrict its practical applications in rechargeable sodium‐ion batteries. Herein, a manganese‐based tunnel‐structured cathode with high rate capability and high initial Coulombic efficiency is prepared by niobium doping and sodium compensation. Via materials characterizations and theoretical calculations, it is demonstrated that a proper amount of niobium doping in tunnel structure can effectively improve its structural stability and charge transport kinetics, resulting in outstanding rate capability (76.6% capacity retained from 0.5 to 30 C) and superior cycling performance (82.3% capacity retention after 800 cycles at 5 C) for the optimized Nb‐doped Na0.44MnO2 cathode (Na0.44Mn0.98Nb0.02O2). Furthermore, NaCrO2 is added into the Na0.44Mn0.98Nb0.02O2 cathode as a self‐sacrificing sodium compensation additive, and a high initial Coulombic efficiency close to 100% is achieved for the composite cathode. This work establishes a facile strategy to design advanced manganese‐based cathode materials for large‐scale energy storage applications.

Structural-phase state and properties of heat and wear resistant cast irons of Cr–Mn–Ni–Ti system additionally alloyed with Al and Nb

The paper presents the data on phase composition and structure forming for the alloys, on distribution of elements among the alloy structural components, on variation of wear resistance, scale resistance, growing stability and mechanical properties of cast iron of Cr–Mn–Ni–Ti–Al–Nb system depending on different aluminium and niobium content and thermal ac-cumulating capacity of a casting mould. Complex carbides (Nb, Ti)C are forming in white cast iron during niobium alloying. Quantitative metallographic analysis of (Nb, Ti)C carbides and (Cr, Fe, Mn)7C3 complex carbides was carried out on the samples with examined composition. Aluminium provides favourable influence on forming of the thin protective spinel-type films with minimal amount of defects; diffusion through such oxide film is very difficult. Joint alloying by aluminium and niobium leads to simultaneous increase of heat resistance and wear resistance. Wear resistance increased as a result of enlargement of the part of primary carbides (Nb, Ti)C with high hardness in the structure of cast iron. Composition of oxide films includes aluminium, which strengthens their protective properties and rises of the alloy scale resistance. It is found for the first time that niobium doping leads to secondary solidification during cooling in the casting mold. Dispersion particles of М7С3 carbides are forming in solid state, thereby no structure degradation occurs during testing at increased temperatures, and growing stability rises. On the basis of the complex of the conducted researches the rational composition of heat and wear resistant cast iron is offered at the following ratio of components, wt. %: 2.1–2.2 C; 4.5–5.0 Mn; 18.0–19.0 Cr; 1.0–1.2 Ni; 0.4–0.6 Ti, 2.0 Nb; 2.0 Al. Wear resistance increased 1.2 times compared to cast irons before the introduction of aluminum and niobium, and scale resistance – 2.4–4.5 times depending on the type of casting mold, the index of growth resistance is equal to zero for cast irons cast in dry SLM

Comparative criticality assessment of a hypothetical fuel element with 316 stainless steel-clad rods doped with niobium through computational simulation

Several applications were explored, including fuel rod coatings, structural alloys, and cooling materials in nuclear reactors, with a focus on performance, safety, and durability improvements. The results revealed that niobium doping provided a range of benefits, such as increased corrosion resistance, greater stability in high-temperature and radiation environments, and contributed to reducing criticality in nuclear fuel elements. These findings underscore the potential of niobium as a strategic material in the nuclear industry, offering promising solutions to the challenges faced in the safe and efficient operation of nuclear reactors, including small modular reactors (SMRs).

Wettability of anatase TiO2 surface: Effect of niobium doping

The effect of niobium doping on the hydrophilic behavior of anatase TiO2 surface was demonstrated on a series of x-Nb-TiO2 nanocoatings with dopant concentrations in the range of 0.0 - 1.0 at.% Nb. Thin films prepared on glass substrates from sols by dip-coating were characterized by tensiometric, work function and isoelectric point measurements along with FT-IR spectroscopy in situ method. Using macroscopic and microscopic techniques, it was found that, at low doping level, it is the functionalization of the anatase surface with niobium ions that leads to a drastic change in its surface acid-base as well as electronic properties and, as a consequence, to a sharp increase in the initial surface hydrophilicity. The rearrangement in the hydroxyl‑hydrated layer with the formation of additional hydroxyl groups as a result of surface functionalization has an increased effect on wettability only at low levels of niobium inclusion, whereas with increasing dopant content the electronic factor plays a significant role on the properties of titanium dioxide, including its wettability. The kinetic dependencies of the photoinduced superhydrophilic conversion for all Nb-doped titanium dioxide surfaces were obtained and discussed in terms of proposed mechanism. Both the initial hydrophilic state and the initial rate of photoinduced hydrophilic conversion depend on the Nb concentration in titanium dioxide, while the final UV-induced superhydrophilic state is achieved for all Nb-doped TiO2 regardless of the dopant content.

Enhanced optical and electrical properties of Nb-doped TiO2 thin films synthesized by atomic layer deposition using the supercycle strategy

Herein, we report highly transparent and conductive Nb-doped TiO2 thin films successfully grown by a thermal ALD process at 300 °C using titanium tetraisopropoxide, niobium(V) ethoxide, and water. The deposition was carried out by employing a supercycle approach, alternating cycles of Ti precursor followed by a monocycle of Nb precursor, thereby enabling precise control over the Nb dopant concentration. We demonstrate the crucial impact of the dopant concentration and annealing conditions played on the thickness, structure, morphology, composition, and optical and electrical properties of the resulting films. The incorporation of niobium dopants led to significant improvements in the film's characteristics. The Nb-doped TiO2 films exhibited an enhanced optical transmission efficiency up to 15 %, along with a remarkable reduction in resistivity by four orders of magnitude, reaching 10−3 Ω.cm, compared to undoped TiO2 films. These high performances establish Nb-doped TiO2 thin films as promising TCOs with wide-ranging applications in fields that require efficient current collection or injection in conjunction with optical radiation transmission.

Investigating the kinetics of small alcohol oxidation reactions using platinum supported on a doped niobium suboxide support

Investigating the kinetics of small alcohol oxidation reactions using platinum supported on a doped niobium suboxide support

The structure of epitaxial growth of Nb-doped ZnO nanorods on intrinsic substrate via sonicated aqueous chemical method

The simplicity and abundance of water sources make water-based synthesis extremely intriguing. Nb-doped ZnO nanorods was successfully grown using a straightforward and cost-effective aqueous chemical technique. The precursor of Nb-doped ZnO comprised zinc nitrate hexahydrate, hexamethylenetetramine (HMTA), and deionized water. These substances were used as starting materials, stabilisers, and solvents, respectively. Niobium chloride served as a source of niobium dopant. The intrinsic seeded substrate was submerged in a Nb-doped ZnO precursor solution in order to facilitate the epitaxial growth of nanorods. In order to investigate the influence of the dopant percentage, the amount of Nb-dopant was varied from 0 to 0.7 at. %. The presence of Nb-doped ZnO nanorods was confirmed by the utilisation of FESEM and EDAX techniques, which allowed for the verification of both the growth of nanorods and the identification of their constituent elements. The diameter obtained is between 79.76 and 134.51 nm, depending on the amount of dopant. Since the average nanorod length is 1.1086 ± 24.9187 μm, the aspect ratio estimation is about 13.9. The atomic arrangement was investigated using high-resolution transmission electron microscopy (HRTEM). The interplanar distance of 0.264 nm corresponds to plan (002) estimated via HRTEM. The estimation is in agreement with the XRD analysis. In addition, the peak of (002) is dominant for every sample. The sharpest and highest peak can be found in 0.3 at. % of dopant. As the texture coefficient (TC) has a higher value for plan (002), crystalline growth is preferred in c-orientation.

A Study on the Microstructure Regulation Effect of Niobium Doping on LiNi0.88Co0.05Mn0.07O2 and the Electrochemical Performance of the Composite Material under High Voltage.

High-nickel ternary materials are currently the most promising lithium battery cathode materials due to their development and application potential. Nevertheless, these materials encounter challenges like cation mixing, lattice oxygen loss, interfacial reactions, and microcracks. These issues are exacerbated at high voltages, compromising their cyclic stability and safety. In this study, we successfully prepared Nb5+-doped high-nickel ternary cathode materials via a high-temperature solid-phase method. We investigated the impact of Nb5+ doping on the microstructure and electrochemical properties of LiNi0.88Co0.05Mn0.07O2 ternary cathode materials by varying the amount of Nb2O5 added. The experimental results suggest that Nb5+ doping does not alter the crystal structure but modifies the particle morphology, yielding radially distributed, elongated, rod-like structures. This morphology effectively mitigates the anisotropic volume changes during cycling, thereby bolstering the material's cyclic stability. The material exhibits a discharge capacity of 224.4 mAh g-1 at 0.1C and 200.3 mAh g-1 at 1C, within a voltage range of 2.7 V-4.5 V. Following 100 cycles at 1C, the capacity retention rate maintains a high level of 92.9%, highlighting the material's remarkable capacity retention and cyclic stability under high-voltage conditions. The enhancement of cyclic stability is primarily due to the synergistic effects caused by Nb5+ doping. Nb5+ modifies the particle morphology, thereby mitigating the formation of microcracks. The formation of high-energy Nb-O bonds prevents oxygen precipitation at high voltages, minimizes the irreversibility of the H2-H3 phase transition, and thereby enhances the stability of the composite material at high voltages.

Effect of niobium doping on excitonic dynamics in MoSe2

Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.

Influence of Doping of Niobium Oxide on the Catalytic Activity of Pt/Al2O3 for CO Oxidation

Pt-based alumina catalysts doped with varying niobium contents (i.e., 0, 1.20, 2.84, and 4.73 wt%, denoted as Pt/Nb–Al2O3) were synthesized via stepwise impregnation for catalytic CO oxidation. The effective incorporation of Nb species without altering the fundamental properties of the Al2O3 support was confirmed by the characterization using XRD, Raman, and TEM. Pt metallic particles were uniformly deposited on the niobium-doped alumina (Nb–Al2O3) support. H2-TPR and CO–TPD analyses were performed to reveal the influence of niobium doping on catalyst reduction and CO adsorption properties. The results consistently demonstrate that the doping of niobium affects reducibility and alleviates the competitive adsorption between CO and O2 during the CO reaction. Particularly, when compared to both undoped and excessively doped Pt/Al2O3 catalysts, the catalyst featuring a 2.84 wt% Nb content on Pt1.4/Nb2.8–Al2O3 displayed the most promising catalytic performance, with a turnover frequency of 3.12 s−1 at 180 °C. This superior performance can be attributed to electron transfer at the Pt/NbOx interface.

Optimizing the Structure and Optical Properties of Lanthanum Aluminate Perovskite through Nb5+ Doping.

This work involves the introduction of niobium oxide into lanthanum aluminate (LaAlO3) via a conventional solid-state reaction technique to yield LaAlO3:Nb (LaNbxAl1-xO3+δ) samples with Nb5+ doping levels ranging from 0.00 to 0.25 mol%. This study presents a comprehensive investigation of the effects of niobium doping on the phase evolution, defect control, and reflectance of LaNbxAl1-xO3+δ powder. Powder X-ray diffraction (XRD) analysis confirms the perovskite structure in all powders, and XRD and transmission electron microscopy (TEM) reveal successful doping of Nb5+ into LaNbxAl1-xO3+δ. The surface morphology was analyzed by scanning electron microscopy (SEM), and the results show that increasing the doping concentration of niobium leads to fewer microstructural defects. Oxygen vacancy defects in different compositions are analyzed at 300 K, and as the doping level increases, a clear trend of defect reduction is observed. Notably, LaNbxAl1-xO3+δ with 0.15 mol% Nb5+ exhibits excellent reflectance properties, with a maximum infrared reflectance of 99.7%. This study shows that LaNbxAl1-xO3+δ powder materials have wide application potential in the field of high reflectivity coating materials due to their extremely low microstructural defects and oxygen vacancy defects.

Niobium doping of CVD-WS2 monolayers using solid precursors with and without salt-KBr as a catalyst: A comparative study

The in situ doping of tungsten disulfide (WS2) monolayers with Niobium (Nb) atoms was obtained through the atmospheric pressure chemical vapor deposition (APCVD) method by controlling the Nb2O5 and WO3 precursors mass ratios. Samples were prepared employing the same growth parameters with and without the use of KBr salt as a catalyst. In both cases, the Nb incorporation quenches the luminescence intensity of the doped samples, and it depends on the Nb2O5:WO3 mass ratio. X-ray photoelectron spectroscopy (XPS) measurements were performed, and the observed redshift at the Fermi level indicated p-type doping. Nb-doped WS2 monolayers synthesized without the use of the catalyst have lower defect density, as revealed by a careful Raman analysis, and are free of agglomerates on their monolayers’ basal plane. The use of KBr as the catalyst increases the average crystal size but also increases the disorder effects compared with samples prepared without the use of salt. The presence of agglomerates of impurities at the surface of doped samples was observed in samples prepared with the use of salt as a catalyst. The controlled synthesis of p-type WS2 with low defect density is essential for developing electronic and photonic devices based on WS2 material.

Achieving neutral-tinted and energy-efficient electrochromic device enabled by sputtered tungsten-niobium-oxygen film for smart windows

WO3 based electrochromic device (ECD) is becoming the mostly-used one for smart windows, however, in WO3 tinted state, the intrinsically deep blue and strong infrared (IR) light absorption, resulting in a habitant discomfortableness and also an enhanced thermal gain from the heated device surface, severely restrict its diversified applications. Herein, we firstly conduct a kind of columnarly-grown and amorphous WO3 film with high concentration of niobium doping (Nb/(Nb+W) = 54.1 at.%). This film is fabricated via sputtering a home-made ceramic target, and subsequently improved by a rapid thermal annealing (RTA) process. Comparing with the conventional WO3, the newly-established system owns not only basic EC properties comprising large light modulation range, fast response, and long-term electrochemically cyclic stability, but also a neutral-tinted color (a* = −1.5, b* = 1.0) as well as a relatively lower IR absorption (63.7 %) in tinted state. These outstanding performances enable the assembled ECD with neutral color (a* = 0.6, b* = −2.7) and a higher energy efficiency in cutting down the interior space air temperature about 4.3 °C in its fully-tinted state, underscoring the potential of the tungsten-niobium-oxygen for commercially viable ECDs.

Influence of niobium and hafnium doping on the wear and corrosion resistance of coatings based on ZrN

The properties of coatings based on the ZrN system with the introduction of hafnium and zirconium (ZrN, (Zr,Nb)N and (Zr,Hf)N), deposited on a Ti6Al–4V titanium alloy substrate are compared. Coatings are deposited by controlled accelerated arc-physical vapor deposition, and the structure of the coatings is studied using a transmission electron microscope. A comparison is made of both the mechanical (hardness, wear resistance, scratch strength) and anticorrosion (in a 3 % solution of NaCl) properties. The (Zr,Hf)N coating (22 at% Hf and 78 at% Zr) has the maximum hardness (HV, 3225 ± 73) and wear resistance. This coating also exhibits higher corrosion resistance. In contrast, introducing Nb into the coating composition reduces the corrosion resistance. This combination of beneficial properties makes the (Zr,Hf)N coating useful for conditions in which the surfaces of parts must simultaneously have high wear resistance, strength, and corrosion resistance.

Niobium doping effect on electrical and optical properties of ZnO nanorods produced by ultrasonic spray pyrolysis

Niobium metal doped ZnO nanorods were fabricated on a glass substrate using an ultrasonic spray pyrolysis system in two steps. The structural, morphological, and optical properties of the produced samples were investigated via an x-ray diffractometer (XRD), a field emission scanning electron microscopy (FE-SEM) combined with energy dispersive x-ray spectroscopy (EDX), and a spectrophotometer, respectively. The XRD patterns were indexed in the hexagonal (wurtzite) unit cell type for all the ZnO samples. In addition, according to the XRD peaks, the crystals grew in the c-axis (002) direction. The morphological features of the obtained thin films were examined. From the SEM micrographs, it was observed that ZnO thin films doped with Nb had a nanorod structure in the c-axis direction. The presence of Nb ions in the samples was proved via EDX analysis. The electrical conductivity values of the pristine and 10 % mol Nb-doped ZnO samples were 3.16 x 10−9 and 3.98 x 10−7 (ohm−1.cm−1) at 25 °C; and 7.08 x 10−7 and 5.01 x 10−5 (ohm−1.cm−1) at 300 °C, respectively. The optical transmittances of the samples were measured at wavelengths of 350–1000 nm. It was observed that the produced films had high optical transparency. The average optical transmittance value of the samples was 90 %.

Dielectric and ferroelectric characterization of niobium doped pzt (52/48) nanoceramics

High performance ferroelectric materials have attracted more attention due to its superior dielectric, piezoelectric, and electrostrictive properties. A sol-gel synthesis technique was used to prepare the perovskite Pb(Nbx(Zr0.52Ti0.48)(1−x))O3 (where x = 0, 0.02) nanoceramics. X-ray powder diffraction studies confirm the successful formation of perovskite (ABO3) structure of the ceramics without presence of pyrochlore (A3B4O13) phase which is unwanted for PZT system. Also, the thermogravimetric studies were conducted to confirm the structure formation at elevated temperature. The relative permittivity increases with doping of niobium and curie temperature decreases for the same. The dielectric study of the undoped PZT at the temperature of 500 °C and Nb doped PZT at the temperature of 350 °C for the same frequency of 100 Hz give relative permittivity, εr ≈ 11000 and εr ≈ 1850 respectively. An Arrhenius plot was used to calculate the activation energy and it was found to be 0.210, and 0.161 eV for the undoped and Nb-doped PZT ceramics respectively. The maximum remnant polarization is 1.21 μC/cm2 for niobium doped PZT and 0.16 μC/cm2 for undoped PZT for the applied voltage of 1500 V. The primary goal of this research is to determine how doping with niobium affects the dielectric and ferroelectric properties of PZT (52/48).